The present invention relates to an impact-less printing device and process and more particularly an impact-less printing device with transfer of ink, of the type wherein an inking substance which is deposited on a movable carrier is transferred to the paper by means of selectively actuated printing elements which are arranged in contact with the sheet of paper on which printing is to be effected.
Various processes and devices for impact-less printing with transfer of ink are known; in one of these, which is described in U.S. Pat. No. 3,989,131 assigned to the same assignee, a print head carries a plurality of suitably spaced and aligned thermo-elements. The head is pressed against a sheet of normal paper with the interposition of a heat-sensitive inking ribbon which is displaced from a feed or unwinding spool to a receiving spool. Whenever a thermoelement is heated by means of a current pulse, a portion of transferrable material is softened and transferred from the ribbon on to the paper, to form a visible recording mark.
In another impact-less printing device of the above-indicated type as described in U.S. Pat. No. 3,570,380 assigned to the same Assignee, a ribbon bearing the apertured symbols to be printed is wound on a hollow transparent drum which is rotatable on two pairs of rollers. A thermographic ribbon which is covered with heat-transferrable material and which is fed from a feed spool passes between the covered surface of the drum and a co-operating roller, and is rewound on to a receiving spool. A sheet of normal paper is passed between the inking ribbon and the co-operating roller. A laser generator is arranged within the drum and selectively projects a beam of radiant energy through the openings of the perforated ribbon against the inking ribbon to transfer portions of inking substance on to the paper, by a thermal effect. In both the above-described known devices, the inking ribbon in each printing operation gives up a portion of inking material so that, once it has been used, it cannot be recovered and must be replaced.
Another process for impact-less printing of the above-mentioned type is that described in U.S. Pat. No. 3,550,153 wherein a sheet of normal paper is disposed above a nylon fabric impregnated with a mixture of alcohol and carbon powder. A pair of electrodes which are disposed on opposite sides with respect to the paper and the fabric are activated by a voltage pulse of the order of 350 volts for a period of 30 nanoseconds.
The electrical field which is thus generated between the two electrodes causes separation of electrified particles of carbon from the nylon fabric, and the transfer thereof onto the paper, at a position corresponding to the character which is formed in relief on the negative electrode. In this case also the carbon-impregnated fabric which is generally in ribbon form must be replaced after being used once, by another fresh ribbon.
U.S. Pat. No. 3,427,633 describes an electrostatic printing device wherein a support of inking material of regenerable type which is formed by a fabric ribbon closed in an annular or ring configuration and impregnated with ink is moved between the paper and the electrodes of a print head. In the return movement, in the direction of the motion, the ribbon passes into a regeneration container filled with pasty inking material which is spread on the ribbon by a blade. Subsequently, outside of the regeneration container, two pairs of rollers put the inking material into a uniform layer on the ribbon. This arrangement suffers from the disadvantage that irregular and more abundant spreading of ink by the blade can clog the rollers, producing therearound an excess of ink which can drip on to other important parts of the machine.